Note: The terms “Foley catheter”, “bladder catheter”, “urinary catheter” or simply “catheter” are used interchangeably throughout this document.
For simplicity of the description, the present invention will mainly be explained in connection with urine flow measurement. The same or similar ideas, apparatuses, techniques, circuits and methods can be used or adopted for the measurement of other fluids in general and other body fluids in particular such as blood or intravenous solution.
In many cases during patient treatment it is necessary to collect and determine continuously the accurate amount of discharged urine from the patient's body. This is routinely done for patients during operations, post-operative patients, patients in intensive care units (ICU), as well as those with urologic disorders where, for example, urine output is directly related to renal function. This type of procedure for collecting, measuring and monitoring urine takes on extreme importance because, for example, sudden changes in urine flow, which can occur at any time, can indicate that there is a deteriorating clinical condition in the patient. Changes in urine output have been correlated with changes in cardiac output. The invasive collection of urine and measurement of urine output are typically accomplished by first catheterizing the patient, i.e. a catheter is passed through the urethra of the patient into the bladder. The other end of the catheter is connected to a container or drainage bag through a length of flexible tubing. Typically the bag is supported below the patient from the patient's bed or other support system such as a wheelchair, and urine drains by gravity force from the patient through the flexible tubing and into the collection bag (FIG. 1). In addition to monitoring urine output as a function of time, the reservoir of a collection bag fills to capacity at unpredicted intervals and someone must empty or replace the bag so it can fill once again with urine. Patients can sometimes obstruct the flow of urine into the bag by lying on the drain tube. Further, if there is blood in the urine, blood clots can form that may clog the catheter. In these cases, no urine appears in the bag after an expected time period. Both a filled bag and blocked tube can cause urine backup and a backup could cause deleterious effect on the patient's condition. For all the above and other reasons, monitoring collection bags and accurately and reliably measuring the urine flow is an important part of providing effective patient therapy.
In order to measure the patient's urine discharge, the urine drainage bag typically has measurement graduation marking on the bag's wall. Once in a predetermined amount of time (e.g. one hour), the nurse or doctor visually checks the urine level in the bag according to the marking and records it in a table in the patient's file. When a more accurate urine flow measurement is required, the measurement is done using a measuring device (FIG. 2). The device is placed in between the catheter and flexible tubing that leads the urine from the bladder, and the urinary drainage bag (FIG. 3). One such device (FIG. 2) is a container that has a volume of about 100-300 ml, and is made of transparent material with graduated markings (21) along its height. The container has an inlet on the top that connects to the tubing (24) carrying the urine from the bladder catheter and an outlet (26) with a valve (27) on the bottom of the container connected to the drainage bag. Initially, the valve at the bottom of the container is placed in the closed position and all the urine that flows from the bladder is being collected in the container. Other designs of such a measuring device are connected in other ways to the drainage bag, for example, with a tube connected from the top of the container to the drainage bag. An example of such a device is described in U.S. Pat. No. 3,345,980. Once in a predetermined time interval (e.g. one hour), the nurse or doctor checks the amount of urine that was collected during that period of time according to the urine liquid level in the container and records it in a table in the patient's file. After the urine volume is read, they then pour the urine accumulated in the container to the drainage bag, either by opening the valve on the bottom of the container or by tilting the container and letting the urine flow through the tubing that connects to the drainage bag or in any other way depending on the type of measuring device used. After emptying the measuring container, it is ready for a new measuring cycle of the predetermined amount of time.